Mixed flow fan is a new type fan between axial flow fan and centrifugal fan with both advantages of them. It possesses larger wind pressure than axial flow fan and blast capacity than centrifugal fan. It has the characteristics of axial flow of air, wide efficient operation area, little noise, compact structure, easy installation, low price and so on. Efficient and low-noise mixed flow fan of SEF type is widely applied in ventilation of civil buildings, diverse working condition such as refrigeration house, textile plant. It can substitute for low pressure centrifugal fan.